Alternating current electromagnet



953 J. F. H. DOUGLAS ETAL 2,648,034

ALTERNATING CURRENT ELECTROMAGNET Filed April 2, 1948 A) awn/r5 RANGEBIEN i U 550 am C'O/L C u/vs r04 ma:

0 R K RANGE o e-u (16550 was E ZXMWML XMMX %\%M Patented Aug. 4, 1953ALTERNATING CURRENT ELECTROMAGNET John F. H. Douglas, Milwaukee, andClarence T. Evans, Wauwatosa, Wis., assignors to Cutler- Hammer, Inc.,Milwaukee, Wis., a corporation of Delaware Application April 2, 1948,Serial No. 18,578

4 Claims.

This invention relates to alternating current operating magnets fordevices such as contactors and relays, and more particularly to controlcir-.

cuits therefor.

As is well known, it is usually desirable in electromagneticallyoperated devices of various types such as contactors and relays that thepull of the operating magnet at all points in its stroke besubstantially equal or only slightly in excess of the load offered bythe operated device. One reason for this requirement is that excessivepull by the operating magnet at any point in its stroke is likely tocause excessive acceleration of the moving parts of the device, which inturn results in noisy operation of the device and undue wear of themagnet parts. However, it is frequently diiiicult in A. C. magnetoperated devices to obtain a pull characteristic in the operating magnetwhich suits the load characteristic of the operated device.

The present invention has among its objects to provide an improvedcontrol circuit for A. C. magnet operated devices which enablesadjustment of the pull characteristic of the operating magnet to suitvarious load conditions encountered in the operated device.

Another object is to provide a control circuit for A. C. magnets whichenables adjustment of the pull characteristic of the magnet by controlof the terminal voltage of the magnet coil at more than two points inthe magnet stroke with a. constant supply voltage.

Various other objects and advantages of the invention will hereinafterappear.

The accompanying drawing illustrates an embodiment of the inventionwhich will now be described, it being understood that the embodimentillustrated is susceptible of modification. without departing from thespirit and scope of the appended claims.

In the drawing,

Figure 1 is a diagrammatic view of an A. C. magnet operated switchhaving a control circuit embodying the invention associated therewith;and

Figs. 2 and 3 are graphic representations of certain characteristics ofthe embodiment shown in Fig. 1.

Referring to Fig. l, a control circuit embodying the invention is shownin connection with an A. C. operating magnet 2 to be supplied withcurrent from an A. C. supply circuit indicated by lines L L Theoperating magnet shown may be of any conventional type, and as shown thesame is provided with an energizing coil 3 which is mounted within alaminated field member 4 of rectangular shape having an opening in thelower side thereof for receiving a laminated armature 5. Armature 5 isnormally held by gravity in the open position illustrated in the drawingand is movable upwardly within coil 3 into a closed position wherein itsupper end seals with field member 4. As illustrated, armature 5 carriesa yielding contact 6 which engages a pair of cooperating stationarycontacts ii during upward movement of said armature into closedposition. Armature 5 also has normally open auxiliary contacts 1associated therewith which are closed during final movement of saidarmature into its closed position.

The control means for magnet 2 includes a condenser 8, a resistance 9, anormally open push button switch I 0 and a normally closed push buttonswitch ll. As shown one terminal of coil 3 is connected to line L inseries with condenser 8 and resistance 9 and the other terminal thereofis connected to line L in series with push button switches l0 and H.Upon depression of push button switch I0, coil 3 is connected acrosslines L L in series with condenser 8 and resistance 9 for response ofarmature 5. Upon release of push button 10, coil 3 is maintainedenergized through the medium of push button switch II and auxiliarycontacts 1, pending opening of push button switch I l.

Referring now to Fig. 2, curve A represents the load imposed on armatur5 during movement thereof into closed position. It is assumed that thepull of armature 5 throughout its stroke varies as illustrated by curveB in Fig. 2 when a constant A. C. voltage is applied to the terminals ofcoil 3. It will be observed from curve B that the pull of armature 5 inits open position is greater than that required for operation of theload, whereas at point C in the armature stroke the pull is insufficientfor operation of the load. In accordance with the present inventioncondenser 8 and resistance 9 are connected in series in the energizingcircuit of coil 3 to decrease the pull of the armature when the same isin open position, and to increase the pull thereof at point C in itsstroke to thereby provide a pull characteristic indicated by dottedcurve D which is desired for proper operation of the load.

The effect of condenser 8 and resistance 9 in the energizing circuit ofthe magnet will now be more fully set forth in connection with Fig. 3.In this figure it is assumed that the desired pull characteristic ofarmature 5 represented by curve D in Fig. 2 is obtained when coil 3 issubjected to a voltage E in the open position of armature 5, a voltage Fat point C in the armature stroke, and a voltage G corresponding to theline voltage when said armature is moved into closed position.

As is well known, the inductive reactance of coil 3 is a function of theposition of armature 5 and is in general higher in the closed positionof said armature than in the open position thereof. Also as is wellknown, the impedance of the energizing circuit of coil 3 is reduced atany point in the armature stroke where the capacitive reactance ofcondenser 8 is less than twice the inductive reactance of coil 3, and isincreased at any point in the armature stroke where the capacitivereactance of said condenser exceeds twice the inductive reactance ofsaid coil. The greatest reduction in impedance is obtained at any pointin the armature stroke where the capacitive reactance of condenser 8equals the inductive reactance of coil 3 and the magnet circuit is thensaid to be resonant.

The voltage across coil 3 is increased to increase the armature pu-ll atany point in the magnet stroke where the impedance of the magnet circuitis reduced, and conversely the voltage across said winding is reduced todecrease the armature pull at any point in the armature stroke where theimpedance of the magnet circuit is increased. Thus if the magnet circuitis rendered resonant at an intermediate point in the armature stroke,coil 3 will be subjected to a high peak resonant voltage at such pointand will also be subjected to voltages of lower value in the open andclosed positions of the armature.

If resistance 9 is not included in the armature circuit it is possible,with a suitable number of turns on coil 3, to proportion the capacitivereactance of condenser ii relative to the inductive reactance of saidcoil to render the mag net circuit resonant at such a point in thearmature stroke that the desired coil voltages E and G are obtained inthe open and closed positions of armature 5. However, the voltage ofcoil 3 then varies throughout the magnet stroke as illustrated by curveH in Fig. 3 and assumes a value I at point C in the armature strokewhich may be considerably higher than the desired voltage F. It is alsopossible with a suitable number of turns on coil 3 to proportion thecapacitive reactance of condenser 8 relative to the inductive reactanceto said coil to render the magnet circuit resonant at such a point inthe armature stroke that the desired coil voltage F is obtained at pointC in the armature stroke and the desired coil voltage G is obtained inthe closed position of the armature. However, the voltage of coil 3 thenvaries throughout the magnet stroke, as illustrated by curve J in Fig. 3and assumes a value K in the open position of armature 5 which may beconsiderably higher than the desired voltage E.

In practice it has been found that if resistance 9 is not included inthe magnet circuit it is impossible to control the impedance of suchcircuit by means of condenser 8 so that the voltage values E, F and Gare obtained in coil 3 at three points in the armature stroke to providethe desired pull characteristic of the magnet illustrated by curve D inFig. 2. However, it has been found that when condenser 8 and resistance9 are both included'in the magnet circuit it is possible to control theimpedance of such circuit for desired voltage values of coil 3 at threepoints in the armature stroke. For example, it has been found that witha suitable number of turns on coil 3 it is possible to adjust resistance9 and the capacitive reactance of condenser 8 to maintain the voltage ofcoil 3 at values E and G in the open and closed positions of armature 5and to also maintain the voltage of said coil at value F at point C inthe armature stroke. When this is done the voltage of coil 3 throughoutthe magnet stroke varies as illustrated by curve L in Fig. 3 to providethe desired pull characteristic of the magnet illustrated by curve D inFig. 2.

From the foregoing, it will be observed that in practice of theinvention it is possible to increase the magnetic pull exerted on thearmature in an intermediate portion of its stroke and maintain the sameor decrease the pull on the armature in open position, while maintainingthe pull on the armature in closed position at the same value obtainablewhen the armature coil is connected directly across the voltage source.In the appended claims such increase in pull in an intermediate portionof the stroke, and decrease in pull in open position, is definedrelative to such unchanged closed position pull. The term increasedrelative to is to be construed to mean that the pull on the armature inan intermediate portion of its stroke is greater than the pull over thecorresponding portion of the armature stroke obtainable when thearmature coil is connected directly across the voltage source. The termdecreased relative to is to be construed to mean that the pull on thearmature in open position is made less than the pull in thecorresponding open position when the armature coil is connected directlyacross the voltage source.

What we claim as new and desire to secure by Letters Patent is:

l. The method of modifying the Dull characteristic of an electromagnethaving an armature movable between an open position and a closedposition, and a coil energized from a source of alternating voltage,which method may be practiced without modifying-the magnetic pull on thearmature in closed position and which consists in including capacitancein series with the coil to increase relative to the magnetic pull on thearmature in closed position the magnetic pullon the armature throughoutan intermediate portion of its range of motion and in coordinating withthe coil and the capacitance series resistance of such value that themagnetic pull on the armature in open position is not increased relativeto the .magnetc pull thereon in closed position.

2. The method of modifying the pull characteristicof an electromagnethaving an armature movable between an open position and a closedposition, and a coil energized from a source of alternating voltage,which consists in including capacitance in series with the coil toincrease relative to the magnetic pull on the armature in closedposition the magnetic pull on the armature throughout an intermediateportion of its range ofmotionandin coordinating with the coil and thecapacitance series resistance of such value that themagneticpull on thearmature in open position is reduced relative to the magnetic pullthereon in closed position, assuming a magnetic pull on the armatureinclosed position such as that obtainable with the same electromagnetrelieved of the aforesaid modifying influences.

3. The combination with an electromagnet having an armature movablebetween open and closed positions and a coil, a source of alternatingvoltage ,to whichsaid coil is connected, a

capacitor series related to said coil. said coil and capacitorrespectively having a number of turns and capacitance value such thatthe magnetic pull on said armature for an intermediate portion of itsstroke is increased relative to the magnetic pull on said armature inits closed position, and a resistor in series with said coil and saidcapacitor, said resistor being of a resistance value such that themagnetic pull on said armature in open position is not increasedrelative to the magnetic pull thereon in closed position, the foregoingusing for reference such magnetic pull on the armature in closedposition as that obtainable With the electromagnet relieved of theaforesaid influence of said capacitor and resistor.

4. The combination with an electromagnet having an armature movablebetween open and closed positions and a coil, a source of alternatingvoltage to which said coil is connected, a capacitor series related tosaid coil, said coil and capacitor respectively having a number of turnsand capacitance value such that the magnetic pull on said armature foran intermediate portion of its stroke is increased relative to themagnetic pull on said armature in its closed position, and

a resistor in series with said coil and said capacitor, said resistorbeing of a resistance value such that the magnetic pull on said armaturein open position is decreased relative to the magnetic pull thereon inclosed position, the foregoing using for reference such magnetic pull onthe armature in closed position as that obtainable with theelectromagnet relieved of the aforesaid influence of said capacitor andresistor.

JOHN F. H. DOUGLAS.

CLARENCE T. EVANS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,040,677 Suits May 12, 1936 2,131,424 Bechberger Sept. 27,1938 2,402,573 Pell June 25, 1946 2,404,982 Owens July 30, 1946 FOREIGNPATENTS Number Country Date 379,711 Great Britain of 1931 602,989Germany Sept. 20, 1934

